Probing the influence of crosslinkers on the properties, response, and degradation of enzymatic hydrogels for electrochemical glucose biosensing through fluorescence analysis

Drop-cast crosslinked hydrogels are a common platform for enzymatic electrochemical biosensors. Despite the widespread use of these complex systems, there are still several questions about how their physicochemical properties affect their performance, stability, and reproducibility. In this work, first-generation faradaic biosensors composed of glucose oxidase and branched polyethyleneimine (BPEI) are prepared using either glutaraldehyde (GA) or ethylene glycol diglycidyl ether (EGDGE) as crosslinkers. While EGDGE gels present an increasing electrochemical response with increasing crosslinker concentration, the current of GA gels decreases at high crosslinker concentration probably due to the hampered diffusion on tightly networked gels. We compared different strategies to use fluorescence microscopy to gain insight into the gel structure either by labeling the gel components with fluorophores or taking advantage of the intrinsic fluorescence of the imines formed upon crosslinking with GA. By monitoring the fluorescence of the crosslinking bonds and the electrochemical response, we demonstrate that hydrolysis, a common hydrogel degradation mechanism, is not responsible for the loss of electrical current over time in gels prepared with glutaraldehyde. Most hydrogel-based electrochemical biosensor studies do not perform specific experiments to determine the cause of the degradation and instead just infer it from the dependence of the current on the preparation conditions (most commonly concentrations). We show that, by taking advantage of several analytical techniques, it is possible to gain more knowledge about the degradation mechanisms and design better enzymatic biosensors.

Selection of highly specific aptamers to Vibrio parahaemolyticus using cell-SELEX powered by functionalized graphene oxide and rolling circle amplification

Cell-SELEX is a powerful tool to screen aptamers binding to living cellular organisms such as bacteria, fungi and even oncocytes. Here, we developed an advanced cell-SELEX strategy featuring functionalized graphene oxide (GO) and isothermal rolling circle amplification (RCA) to select aptamers against a prevailing foodborne pathogen, Vibrio parahaemolyticus. Polyethyleneglycol (PEG) and chitosan (CTS) were grafted onto the sheet-like GO molecules to synthesize a PC-GO material. TEM and FT-IR characterization demonstrated that the PC-GO composites were near-nanometric scale and tethered with PEG and CTS moieties, a property that significantly improved its solubility in biological buffer solutions used in cell-SELEX process. PC-GO could bind with ssDNAs with lower affinities to target cells, therefore the selection efficiency is greatly enhanced. The cell-binding aptamer candidates (CACs) were amplified by 10⁷ fold using complementary ring mediated (CRM-RCA), a created amplification method that generate single-stranded products, which could be directly used in the next round selection. As fueled by PC-GO and CRM-RCA, four highly specific aptamers with lowest K_d value of 10.3 ± 2.5 nM were obtained. Flow cytometry analysis showed that all the four aptamers exhibited more than 75% binding affinity to V. parahaemolyticus than to other foodborne bacteria (less than 18%). Simple procedure, high efficiency, and free from expensive thermal cycler (required by PCR amplification) will enable the established strategy to find its applications in aptamer selecting against fungi, stem and cancerous cells as well.

Synthesis, crystal structure and hydrolysis activity of a novel heterobinuclear cobalt(ІІІ) sodium(І) Schiff base complex

A novel heterobinuclear complex [CoNa(C₁₅H₁₀NO₄F)₂(CH₃OH)]₂ with Schiff base (C₁₅H₁₀NO₄F: 2-amino-4-fluorobenzoic acid-3-methoxysalicylaldehyde) was synthesized and characterized by IR and ¹H NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. X-ray crystallography reveals that the cobalt atom is six-coordinated by two nitrogen atoms from -CN-, two carboxylate oxygen atoms and two hydroxyl oxygen atoms in different ligands, while the sodium atom is seven-coordinated by two methoxy oxygen atoms, two hydroxyl oxygen atoms in different ligands, two oxygen atoms in the same carboxylate and one oxygen atom of solvent methanol. The reaction results of the complex with the p-nitrophenylphosphate (pNPP) and the adenosine monophosphate (AMP) reveal that the complex can hydrolyze phosphoester bonds. Then the DNA-hydrolysis activity is studied experimentally and theoretically, indicating that the complex can effectively hydrolyze the pBR322 supercoiled plasmid DNA. The molecular docking technology predicts the best binding site and binding affinity between the complex and DNA, and then the catalytic mechanism of hydrolysis is supposed. The study results suggest that the Schiff base metal complex, as a potent artificial enzyme, may find its applications in catalytic hydrolysis and biotechnological areas.

Theoretical and experimental studies on the separation of cinnamyl acetate and cinnamaldehyde by adsorption onto a β-cyclodextrin polyurethane polymer

CAc and CA were separated using CDPU as adsorbent, and the mechanism was proposed through DFT calculations and experimental analyses.

Synthesis of a novel chitosan-based Ce(IV) complex with proteolytic activity in vitro toward edible biological proteins

The occurrence of enzymatic activities is attributed to proper spatial organization of functional groups from first principles. A novel chitosan-based Ce(IV) complex (CC[Ce(IV)]), an artificial metalloproteinase, was synthesized by attaching cyclen, Ce(IV), and chlorophyll-Cu(II) to a chitosan-based matrix. The enzymatic hydrolytic efficiency (HE) and the procedure of catalyzing myoglobin (Mb) by CC[Ce(IV)] in vitro were investigated using spectrophotometry, electrophoresis, and liquid chromatography. The results showed that the HE of Mb was up to 60% at 60°C within 24h, displaying a catalytic proficiency. The pseudo-first-order kinetic constant (kobs) for CC[Ce(IV)] treatment within 24h was 3.85×10(-2)h(-1), higher than that for α-chymotrypsin treatment, which was 2.63×10(-2)h(-1). Moreover, the peptide bond derived from Asp-Phe/Phe-Asp in Mb could be specifically cleaved by CC[Ce(IV)], which could simulate the functionality of α-chymotrypsin. This work provides an experimental basis for potential utilization of the chitosan-based Ce(IV) complexes in the food industry.